Continuity mistake: When David confronts "Ramon", at first he shoots the beast (somehow hurting him more than anyone could do throughout the whole movie, even Kelly who practically shot him in the mouth) a few times, gun in the right hand, flashlight in the left hand. He runs then away, gun in the left, flashlight in the right. They swap again later. (01:20:00)
Continuity mistake: The guy that lies dead next to the crushed car at the party has his head tucked more or less closely under the right arm depending on the camera angle. (01:17:55)
Continuity mistake: During the assault on the car, the vehicle rocks violently in some shots, only to appear perfectly still when it cuts from passenger to driver and vice versa. (01:16:50)
Other mistake: In the party scene, the monster chews repeatedly on a blonde man in a white tuxedo while suspiciously humping a table. This happens while Slade locks the car. There's another shot of the partygoers running away scared, but that is recycled from the earlier bit when the alligator tail-whipped a security guard earlier; the guests that are running away are the exact same (look for instance at the woman with the brown dress and the black belt). You can even spot the security guard flying again in the air like a minute earlier. (01:16:25)
Revealing mistake: During the party, one of the security guys shoots the alligator, who then whips him with the tail. The guy flies in the air, and to the left of the screen when he falls there's a string plainly visible to help moving the tail. (01:15:45)
Other mistake: Henry Silva is interviewed by a reporter played by Sue Lyon in her last movie appearance. She holds a microphone with the familiar peacock symbol of NBC on it, but in the end credits she is "ABC Reporter." (00:50:10 - 01:25:45)
Continuity mistake: After the large mudprint of "Ramon" has been found, David has to make his way back from the lake through a crowd of street vendors and weirdos in general spurred by the presence of the big animal. Just before he meets a bald guy that is carting several plush crocodiles, there's some young fella in a blue and red checkered shirt. David walks past this group and in the next shot after a while he runs in the shirt guy again. (00:49:25)
Revealing mistake: A policeman hilariously crashes his car because he was coming in too fast when the kids escaped the molegator. The car that explodes has square, all red emergency lights, but the car that was speeding through the street had red and blue lights of a different shape. (00:44:50)
Revealing mistake: Obvious B-movie special effect when the alligator breaks through the sidewalk, supposedly creating earthquake-like tremors that are simply someone shaking the camera up and down and the cement bends and deforms like cardboard. (00:44:00)
Continuity mistake: When Kelly grabs his coworker's butt, he does it with the left hand in the Jaws-like POV, but then it turns out he's using the right hand and the left hand is the one holding the flashlight. (00:25:00)
Revealing mistake: Gutchel brings in the sewers the animal carcasses using the supermarket cart. He gets inside, then passes a first tunnel, then another one...or rather, passes the exact same tunnel as before, but in the other direction, to make it look like he travelled a bigger length - just check the graffiti on the wall, it's the same one. (00:09:25)
Continuity mistake: When the boss of the laboratory sits on the desk, he moves just the lamp, but the board has moved next to the lighter as well. (00:13:55)
Continuity mistake: Luke Gutchel is at the evil pharmaceutical company. The scientist tells him he wants 'puppies'; it cuts away on him a moment, and the garbage bag has changed position on the cart. (00:08:25)
Continuity mistake: When David opens the manhole to get in the sewers for the last time for the big finale, he is wearing the same blue sneakers he was wearing at the hospital, but as he goes down the ladder he is wearing black boots. (01:19:10)
Continuity mistake: In the humorous bit with Marisa showing up at the gates of the party, her hand is on the window frame or on the steering wheel depending on the camera angle. (01:17:35)
Continuity mistake: The woman next to Slade when he's at the BBQ at the party holds her glass up, down, up in different shots. (01:14:40)
Continuity mistake: At the sour ending of their 'date', Marisa throws a bunch of bills on the table. David's shadow on the wall moves between shots, but he did not. (01:07:45)
Continuity mistake: A guy tries to sell a baby alligator to the protagonist. He approaches it holding the lid of the shoebox in his right hand, but in the reverse shot he's holding it in the left hand. (00:49:40)
Continuity mistake: David is looking at the book about alligators; he holds it with the fingers at the top corner, but in the reverse shot the fingers are not visible in that spot. (00:35:00)
Continuity mistake: When the slimeball reporter is listening to an all-too-chatty nurse, he is leaning against his own hand which is in a different position in the reverse shot. (00:32:20)
